HOPS/TMUB1 Enhances Apoptosis in TP53 Mutation-Independent Setting in Human Cancers.

TP53 mutations are prevalent in various cancers, yet the complexity of apoptotic pathway deregulation suggests the involvement of additional factors. HOPS/TMUB1 is known to extend the half-life of p53 under normal and stress conditions, implying a regulatory function. This study investigates, for the first time, the potential modulatory role of the ubiquitin-like-protein HOPS/TMUB1 in p53-mutants. A comprehensive analysis of apoptosis in the most frequent p53-mutants, R175, R248, and R273, in SKBR3, MIA PaCa2, and H1975 cells indicates that the overexpression of HOPS induces apoptosis at least equivalent to that caused by DNA damage. Immunoprecipitation assays confirm HOPS binding to p53-mutant forms. The interaction of HOPS/TMUB1 with p53-mutants strengthens its effect on the apoptotic cascade, showing a context-dependent gain or loss of function. Gene expression analysis of the MYC and TP63 genes shows that H1975 exhibit a gain-of-function profile, while SKBR3 promote apoptosis in a TP63-dependent manner. The TCGA data further corroborate HOPS/TMUB1's positive correlation with apoptotic genes BAX, BBC3, and NOXA1, underscoring its relevance in patient samples. Notably, singular TP53 mutations inadequately explain pathway dysregulation, emphasizing the need to explore additional contributing factors. These findings illuminate the intricate interplay among TP53 mutations, HOPS/TMUB1, and apoptotic pathways, providing valuable insights for targeted cancer interventions.

A microbially produced AhR ligand promotes a Tph1-driven tolerogenic program in multiple sclerosis.

Multiple sclerosis is a debilitating autoimmune disease, characterized by chronic inflammation of the central nervous system. While the significance of the gut microbiome on multiple sclerosis pathogenesis is established, the underlining mechanisms are unknown. We found that serum levels of the microbial postbiotic tryptophan metabolite indole-3-carboxaldehyde (3-IAld) inversely correlated with disease duration in multiple sclerosis patients. Much like the host-derived tryptophan derivative L-Kynurenine, 3-IAld would bind and activate the Aryl hydrocarbon Receptor (AhR), which, in turn, controls endogenous tryptophan catabolic pathways. As a result, in peripheral lymph nodes, microbial 3-IAld, affected mast-cell tryptophan metabolism, forcing mast cells to produce serotonin via Tph1. We thus propose a protective role for AhR-mast-cell activation driven by the microbiome, whereby natural metabolites or postbiotics will have a physiological role in immune homeostasis and may act as therapeutic targets in autoimmune diseases.

Membrane Localization and Phosphorylation of Indoleamine 2,3-Dioxygenase 2 (IDO2) in A549 Human Lung Adenocarcinoma Cells: First Steps in Exploring Its Signaling Function.

Indoleamine 2,3-dioxygenase 2 (IDO2) is a paralog of Indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan-degrading enzyme producing immunomodulatory molecules. However, the two proteins are unlikely to carry out the same functions. IDO2 shows little or no tryptophan catabolic activity and exerts contrasting immunomodulatory roles in a context-dependent manner in cancer and autoimmune diseases. The recently described potential non-enzymatic activity of IDO2 has suggested its possible involvement in alternative pathways, resulting in either pro- or anti-inflammatory effects in different models. In a previous study on non-small cell lung cancer (NSCLC) tissues, we found that IDO2 expression revealed at the plasma membrane level of tumor cells was significantly associated with poor prognosis. In this study, the A549 human cell line, basally expressing IDO2, was used as an in vitro model of human lung adenocarcinoma to gain more insights into a possible alternative function of IDO2 different from the catalytic one. In these cells, immunocytochemistry and isopycnic sucrose gradient analyses confirmed the IDO2 protein localization in the cell membrane compartment, and the immunoprecipitation of tyrosine-phosphorylated proteins revealed that kinase activities can target IDO2. The different localization from the cytosolic one and the phosphorylation state are the first indications for the signaling function of IDO2, suggesting that the IDO2 non-enzymatic role in cancer cells is worthy of deeper understanding.

Use of CRISPR/CAS9 Technologies to Study the Role of TLR in Dendritic Cell Subsets.

Dendritic cells (DCs) have a significant role in coordinating both innate and adaptive immunity by serving as sentinels that detect invaders and initiate immune responses to eliminate them, as well as presenting antigens to activate adaptive immune responses that are specific to the antigen and the context in which it was detected. The regulation of DC functions is complex and involves intracellular drivers such as transcription factors and signaling pathways, as well as intercellular interactions with adhesion molecules, chemokines, and their receptors in the microenvironment. Toll-like receptors (TLRs) are crucial for DCs to detect pathogen-associated molecular patterns (PAMPs) and initiate downstream signaling pathways that lead to DC maturation and education in bridging with adaptive immunity, including the upregulation of MHC class II expression, induction of CD80, CD86, and CD40, and production of innate cytokines. Understanding the TLR pathways that DCs use to respond to innate immune stimuli and convert them into adaptive responses is important for new therapeutic targets identification.We present a novel platform that offers a fast and affordable CRISPR-Cas9 screening of genes that are involved in dendritic cells' TLR-dependent activation. Using CRISPR/Cas9 screening to target individual TLR genes in different dendritic cell subsets allows the identification of TLR-dependent pathways that regulate dendritic cell activation and cytokine production. This approach offers the efficient targeting of TLR driver genes to modulate the immune response and identify novel immune response regulators, establishing a causal link between these regulators and functional phenotypes based on genotypes.

A back-door insight into the modulation of Src kinase activity by the polyamine spermidine.

Src is a protein tyrosine kinase commonly activated downstream of transmembrane receptors and plays key roles in cell growth, migration, and survival signaling pathways. In conventional dendritic cells (cDCs), Src is involved in the activation of the non-enzymatic functions of indoleamine 2,3-dioxygenase 1 (IDO1), an immunoregulatory molecule endowed with both catalytic activity and signal transducing properties. Prompted by the discovery that the metabolite spermidine confers a tolerogenic phenotype on cDCs that is dependent on both the expression of IDO1 and the activity of Src kinase, we here investigated the spermidine mode of action. We found that spermidine directly binds Src in a previously unknown allosteric site located on the backside of the SH2 domain and thus acts as a positive allosteric modulator of the enzyme. Besides confirming that Src phosphorylates IDO1, here we showed that spermidine promotes the protein-protein interaction of Src with IDO1. Overall, this study may pave the way toward the design of allosteric modulators able to switch on/off the Src-mediated pathways, including those involving the immunoregulatory protein IDO1.

The catalytic inhibitor epacadostat can affect the non-enzymatic function of IDO1.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme chronically activated in many cancer patients and its expression and activity correlate with a poor prognosis. In fact, it acts as an immune regulator and contributes to tumor-induced immunosuppression by determining tryptophan deprivation and producing immunosuppressive metabolites named kynurenines. These findings made IDO1 an attractive target for cancer immunotherapy and small-molecule inhibitors, such as epacadostat, have been developed to block its enzymatic activity. Although epacadostat was effective in preclinical models and in early phase trials, it gave negative results in a metastatic melanoma randomized phase III study to test the benefit of adding epacadostat to the reference pembrolizumab therapy. However, the reason for the epacadostat failure in this clinical trial has never been understood. Our data suggest that a possible explanation of epacadostat ineffectiveness may rely on the ability of this drug to enhance the other IDO1 immunoregulatory mechanism, involving intracellular signaling function. These findings open up a new perspective for IDO1 inhibitors developed as new anticancer drugs, which should be carefully evaluated for their ability to block not only the catalytic but also the signaling activity of IDO1.

A tryptophan metabolite prevents depletion of circulating endothelial progenitor cells in systemic low-grade inflammation.

Background: Chronic systemic inflammation reduces the bioavailability of circulating endothelial progenitor cells (EPCs). Indoleamine 2,3-dioxygenase 1 (IDO1), a key enzyme of immune tolerance catalyzing the initial step of tryptophan degradation along the so-called l-kynurenine (l-kyn) pathway, that is induced by inflammatory stimuli and exerts anti-inflammatory effects. A specific relationship between IDO1 activity and circulating EPC numbers has not yet been investigated. Methods: In this study, circulating EPCs were examined in mice treated with low doses of lipopolysaccharide (LPS) to mimic low-grade inflammation. Moreover, the association between IDO1 activity and circulating EPCs was studied in a cohort of 277 patients with variable systemic low-grade inflammation. Results: Repeated low doses of LPS caused a decrease in circulating EPCs and l-kyn supplementation, mimicking IDO1 activation, significantly increased EPC numbers under homeostatic conditions preventing EPC decline in low-grade endotoxemia. Accordingly, in patients with variable systemic low-grade inflammation, there was a significant interaction between IDO1 activity and high-sensitivity C-reactive protein (hs-CRP) in predicting circulating EPCs, with high hs-CRP associated with significantly lower EPCs at low IDO1 activity but not at high IDO1 activity. Interpretation: Overall, these findings demonstrate that systemic low-grade inflammation reduces circulating EPCs. However, high IDO1 activity and l-kyn supplementation limit circulating EPC loss in low-grade inflammation.

The circadian control of tryptophan metabolism regulates the host response to pulmonary fungal infections.

The environmental light/dark cycle has left its mark on the body's physiological functions to condition not only our inner biology, but also the interaction with external cues. In this scenario, the circadian regulation of the immune response has emerged as a critical factor in defining the host-pathogen interaction and the identification of the underlying circuitry represents a prerequisite for the development of circadian-based therapeutic strategies. The possibility to track down the circadian regulation of the immune response to a metabolic pathway would represent a unique opportunity in this direction. Herein, we show that the metabolism of the essential amino acid tryptophan, involved in the regulation of fundamental processes in mammals, is regulated in a circadian manner in both murine and human cells and in mouse tissues. By resorting to a murine model of pulmonary infection with the opportunistic fungus Aspergillus fumigatus, we showed that the circadian oscillation in the lung of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO)1, generating the immunoregulatory kynurenine, resulted in diurnal changes in the immune response and the outcome of fungal infection. In addition, the circadian regulation of IDO1 drives such diurnal changes in a pre-clinical model of cystic fibrosis (CF), an autosomal recessive disease characterized by progressive lung function decline and recurrent infections, thus acquiring considerable clinical relevance. Our results demonstrate that the circadian rhythm at the intersection between metabolism and immune response underlies the diurnal changes in host-fungal interaction, thus paving the way for a circadian-based antimicrobial therapy.

Microbiota-Associated HAF-EVs Regulate Monocytes by Triggering or Inhibiting Inflammasome Activation.

In pregnancy, human amniotic fluid extracellular vesicles (HAF-EVs) exert anti-inflammatory effects on T cells and on monocytes, supporting their immunoregulatory roles. The specific mechanisms are still not completely defined. The aim of this study was to investigate the ability of HAF-EVs, isolated from pregnant women who underwent amniocentesis and purified by gradient ultracentrifugation, to affect inflammasome activation in the human monocytes. Proteomic studies revealed that HAF-EV samples expressed several immunoregulatory molecules as well as small amounts of endotoxin. Surprisingly, metagenomic analysis shows the presence of specific bacterial strain variants associated with HAF-EVs as potential sources of the endotoxin. Remarkably, we showed that a single treatment of THP-1 cells with HAF-EVs triggered inflammasome activation, whereas the same treatment followed by LPS and ATP sensitization prevented inflammasome activation, a pathway resembling monocyte refractories. A bioinformatics analysis of microbiota-HAF-EVs functional pathways confirmed the presence of enzymes for endotoxin biosynthesis as well as others associated with immunoregulatory functions. Overall, these data suggest that HAF-EVs could serve as a source of the isolation of a specific microbiota during early pregnancy. Moreover, HAF-EVs could act as a novel system to balance immune training and tolerance by modulating the inflammasome in monocytes or other cells.

Immune correlates of protection by vaccine against SARS-CoV-2 in patients with chronic lymphocytic leukaemia.

In chronic lymphocytic leukaemia (CLL) the efficacy of SARS-CoV-2 vaccination remains unclear as most studies have focused on humoral responses. Here we comprehensively examined humoral and cellular responses to vaccine in CLL patients. Seroconversion was observed in 55.2% of CLL with lower rate and antibody titres in treated patients. T-cell responses were detected in a significant fraction of patients. CD4+ and CD8+ frequencies were significantly increased independent of serology with higher levels of CD4+ cells in patients under a Bruton tyrosine kinase (BTK) or a B-cell lymphoma 2 (BCL-2) inhibitor. Vaccination skewed CD8+ cells towards a highly cytotoxic phenotype, more pronounced in seroconverted patients. A high proportion of patients showed spike-specific CD4+ and CD8+ cells producing interferon gamma (IFNγ) and tumour necrosis factor alpha (TNFα). Patients under a BTK inhibitor showed increased production of IFNγ and TNFα by CD4+ cells. Vaccination induced a Th1 polarization reverting the Th2 CLL T-cell profile in the majority of patients with lower IL-4 production in untreated and BTK-inhibitor-treated patients. Such robust T-cell responses may have contributed to remarkable protection against hospitalization and death in a cohort of 540 patients. Combining T-cell metrics with seroprevalence may yield a more accurate measure of population immunity in CLL, providing consequential insights for public health.

Sperm-carried IGF2 downregulated the expression of mitogens produced by Sertoli cells: A paracrine mechanism for regulating spermatogenesis?

Introduction: Insulin-like growth factor 2 (IGF2) mRNA has been found in human and mouse spermatozoa. It is currently unknown whether the IGF2 protein is expressed in human spermatozoa and, if so, its possible role in the cross-talk between germ and Sertoli cells (SCs) during spermatogenesis. Methods: To accomplish this, we analyzed sperm samples from four consecutive Caucasian men. Furthermore, to understand its role during the spermatogenetic process, porcine SCs were incubated with increasing concentrations (0.33, 3.33, and 10 ng/mL) of recombinant human IGF2 (rhIGF2) for 48 hours. Subsequently, the experiments were repeated by pre-incubating SCs with the non-competitive insulin-like growth factor 1 receptor (IGF1R) inhibitor NVP-AEW541. The following outcomes were evaluated: 1) Gene expression of the glial cell-line derived neurotrophic factor (GDNF), fibroblast growth factor 2 (FGF2), and stem cell factor (SCF) mitogens; 2) gene and protein expression of follicle-stimulating hormone receptor (FSHR), anti-Müllerian hormone (AMH), and inhibin B; 3) SC proliferation. Results: We found that the IGF2 protein was present in each of the sperm samples. IGF2 appeared as a cytoplasmic protein localized in the equatorial and post-acrosomal segment and with a varying degree of expression in each cell. In SCs, IGF2 significantly downregulated GDNF gene expression in a concentration-dependent manner. FGF2 and SCF were downregulated only by the highest concentration of IGF2. Similarly, IGF2 downregulated the FSHR gene and FSHR, AMH, and inhibin B protein expression. Finally, IGF2 significantly suppressed the SC proliferation rate. All these findings were reversed by pre-incubation with NVP-AEW541, suggesting an effect mediated by the interaction of IGF2 with the IGFR. Conclusion: In conclusion, sperm IGF2 seems to downregulate the expression of mitogens, which are known to be physiologically released by the SCs to promote gonocyte proliferation and spermatogonial fate adoption. These findings suggest the presence of paracrine regulatory mechanisms acting on the seminiferous epithelium during spermatogenesis, by which germ cells can influence the amount of mitogens released by the SCs, their sensitivity to FSH, and their rate of proliferation.

Indoleamine 2,3-dioxygenase 1 activation in mature cDC1 promotes tolerogenic education of inflammatory cDC2 via metabolic communication.

Conventional dendritic cells (cDCs), cDC1 and cDC2, act both to initiate immunity and maintain self-tolerance. The tryptophan metabolic enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is used by cDCs in maintaining tolerance, but its role in different subsets remains unclear. At homeostasis, only mature CCR7+ cDC1 expressed IDO1 that was dependent on IRF8. Lipopolysaccharide treatment induced maturation and IDO1-dependent tolerogenic activity in isolated immature cDC1, but not isolated cDC2. However, both human and mouse cDC2 could induce IDO1 and acquire tolerogenic function when co-cultured with mature cDC1 through the action of cDC1-derived l-kynurenine. Accordingly, cDC1-specific inactivation of IDO1 in vivo exacerbated disease in experimental autoimmune encephalomyelitis. This study identifies a previously unrecognized metabolic communication in which IDO1-expressing cDC1 cells extend their immunoregulatory capacity to the cDC2 subset through their production of tryptophan metabolite l-kynurenine. This metabolic axis represents a potential therapeutic target in treating autoimmune demyelinating diseases.

Liver gene therapy with intein-mediated F8 trans-splicing corrects mouse haemophilia A.

Liver gene therapy with adeno-associated viral (AAV) vectors is under clinical investigation for haemophilia A (HemA), the most common inherited X-linked bleeding disorder. Major limitations are the large size of the F8 transgene, which makes packaging in a single AAV vector a challenge, as well as the development of circulating anti-F8 antibodies which neutralise F8 activity. Taking advantage of split-intein-mediated protein trans-splicing, we divided the coding sequence of the large and highly secreted F8-N6 variant in two separate AAV-intein vectors whose co-administration to HemA mice results in the expression of therapeutic levels of F8 over time. This occurred without eliciting circulating anti-F8 antibodies unlike animals treated with the single oversized AAV-F8 vector under clinical development. Therefore, liver gene therapy with AAV-F8-N6 intein should be considered as a potential therapeutic strategy for HemA.

Optimizing therapeutic outcomes of immune checkpoint blockade by a microbial tryptophan metabolite.

BACKGROUND: Despite the great success, the therapeutic benefits of immune checkpoint inhibitors (ICIs) in cancer immunotherapy are limited by either various resistance mechanisms or ICI-associated toxic effects including gastrointestinal toxicity. Thus, novel therapeutic strategies that provide manageable side effects to existing ICIs would enhance and expand their therapeutic efficacy and application. Due to its proven role in cancer development and immune regulation, gut microbiome has gained increasing expectation as a potential armamentarium to optimize immunotherapy with ICI. However, much has to be learned to fully harness gut microbiome for clinical applicability. Here we have assessed whether microbial metabolites working at the interface between microbes and the host immune system may optimize ICI therapy. METHODS: To this purpose, we have tested indole-3-carboxaldehyde (3-IAld), a microbial tryptophan catabolite known to contribute to epithelial barrier function and immune homeostasis in the gut via the aryl hydrocarbon receptor (AhR), in different murine models of ICI-induced colitis. Epithelial barrier integrity, inflammation and changes in gut microbiome composition and function were analyzed. AhR, indoleamine 2,3-dioxygenase 1, interleukin (IL)-10 and IL-22 knockout mice were used to investigate the mechanism of 3-IAld activity. The function of the microbiome changes induced by 3-IAld was evaluated on fecal microbiome transplantation (FMT). Finally, murine tumor models were used to assess the effect of 3-IAld treatment on the antitumor activity of ICI. RESULTS: On administration to mice with ICI-induced colitis, 3-IAld protected mice from intestinal damage via a dual action on both the host and the microbes. Indeed, paralleling the activation of the host AhR/IL-22-dependent pathway, 3-IAld also affected the composition and function of the microbiota such that FMT from 3-IAld-treated mice protected against ICI-induced colitis with the contribution of butyrate-producing bacteria. Importantly, while preventing intestinal damage, 3-IAld did not impair the antitumor activity of ICI. CONCLUSIONS: This study provides a proof-of-concept demonstration that moving past bacterial phylogeny and focusing on bacterial metabolome may lead to a new class of discrete molecules, and that working at the interface between microbes and the host immune system may optimize ICI therapy.

Amniotic fluid stem cell-derived extracellular vesicles are independent metabolic units capable of modulating inflammasome activation in THP-1 cells.

An immunoregulatory role of stem cells, often mediated by their secretome, has been claimed by several studies. Stem cell-derived extracellular vesicles (EVs) are crucial components of the secretome. EVs, a heterogeneous group of membranous vesicles released by many cell types into the extracellular space, are now considered as an additional mechanism for intercellular communication. In this study, we aimed at investigating whether human amniotic stem cell-derived extracellular vesicles (HASC-EVs) were able to interfere with inflammasome activation in the THP-1 cell line. Two subsets of HASC-EVs were collected by sequential centrifugation, namely HASC-P10 and HASC-P100. We demonstrated that HASC-EVs were neither internalized into nor undertake a direct interaction with THP-1 cells. We showed that HASC-P10 and P100 were able to intrinsically produce ATP, which was further converted to adenosine by 5'-nucleotidase (CD73) and ectonucleoside triphosphate diphosphohydrolase-1 (CD39). We found that THP-1 cells conditioned with both types of HASC-EVs failed to activate the NLRP3/caspase-1/inflammasome platform in response to LPS and ATP treatment by a mechanism involving A2a adenosine receptor activation. These results support a role for HASC-EVs as independent metabolic units capable of modifying the cellular functions, leading to anti-inflammatory effects in monocytic cells.

Anakinra restores cellular proteostasis by coupling mitochondrial redox balance to autophagy.

Autophagy selectively degrades aggregation-prone misfolded proteins caused by defective cellular proteostasis. However, the complexity of autophagy may prevent the full appreciation of how its modulation could be used as a therapeutic strategy in disease management. Here, we define a molecular pathway through which recombinant IL-1 receptor antagonist (IL-1Ra, anakinra) affects cellular proteostasis independently from the IL-1 receptor (IL-1R1). Anakinra promoted H2O2-driven autophagy through a xenobiotic sensing pathway involving the aryl hydrocarbon receptor that, activated through the indoleamine 2,3-dioxygenase 1-kynurenine pathway, transcriptionally activated NADPH oxidase 4 independent of the IL-1R1. By coupling the mitochondrial redox balance to autophagy, anakinra improved the dysregulated proteostasis network in murine and human cystic fibrosis. We anticipate that anakinra may represent a therapeutic option in addition to its IL-1R1-dependent antiinflammatory properties by acting at the intersection of mitochondrial oxidative stress and autophagy with the capacity to restore conditions in which defective proteostasis leads to human disease.

Liver-Directed Adeno-Associated Virus-Mediated Gene Therapy for Mucopolysaccharidosis Type VI.

Gene Therapy for Mucopolysaccharidosis Type VIIn this open-label gene therapy study, infusions for MPS type VI occurred without severe adverse events. In the high-dose cohort, serum active arylsulfatase B reached 30% to 100% of normal. A modest urinary GAG increase did not require reintroduction of enzyme replacement therapy. Clinical deterioration was not noted for up to 2 years after therapy.

Prevalence of vitamin D deficiency and its prognostic impact on patients hospitalized with COVID-19.

OBJECTIVES: Although hypovitaminosis D appears to be highly prevalent in patients with coronavirus disease 2019 (COVID-19), its impact on their prognosis remains unclear. METHODS: In this study, serum 25-hydroxyvitamin D (Vit-D) level was measured in 200 patients hospitalized with COVID-19. The association between Vit-D and the composite endpoint of intensive care unit (ICU) admission/in-hospital death was explored using univariable and multivariable analyses. Also, serum Vit-D level in patients with COVID-19 was compared with that in age- and sex-balanced COVID-19-negative controls (i.e., 50 inpatients with sepsis). RESULTS: Serum Vit-D level was comparable between patients with COVID-19 and COVID-19-negative inpatients with sepsis (P = 0.397). No significant differences were found in serum Vit-D level according to COVID-19 severity at the time of hospital admission (P = 0.299). Incidence rates of the composite endpoint of ICU admission/in-hospital death did not differ significantly between patients with either Vit-D deficiency (i.e., Vit-D <20 ng/mL) or severe Vit-D deficiency (i.e., Vit-D <12 ng/mL) and those without (31% vs 35% with P = 0.649, and 34% vs 30% with P = 0.593, respectively). Vit-D level and status (i.e., Vit-D deficiency and severe Vit-D deficiency) were not prospectively associated with the risk of the composite endpoint of ICU admission/in-hospital death (P > 0.05 for all Cox regression models). CONCLUSIONS: Regardless of the potential usefulness of Vit-D measurement to guide appropriate supplementation, Vit-D does not appear to provide helpful information for the stratification of in-hospital prognosis in patients with COVID-19.

3-hydroxy-L-kynurenamine is an immunomodulatory biogenic amine.

Tryptophan catabolism is a major metabolic pathway utilized by several professional and non-professional antigen presenting cells to maintain immunological tolerance. Here we report that 3-hydroxy-L-kynurenamine (3-HKA) is a biogenic amine produced via an alternative pathway of tryptophan metabolism. In vitro, 3-HKA has an anti-inflammatory profile by inhibiting the IFN-γ mediated STAT1/NF-κΒ pathway in both mouse and human dendritic cells (DCs) with a consequent decrease in the release of pro-inflammatory chemokines and cytokines, most notably TNF, IL-6, and IL12p70. 3-HKA has protective effects in an experimental mouse model of psoriasis by decreasing skin thickness, erythema, scaling and fissuring, reducing TNF, IL-1ß, IFN-γ, and IL-17 production, and inhibiting generation of effector CD8+ T cells. Similarly, in a mouse model of nephrotoxic nephritis, besides reducing inflammatory cytokines, 3-HKA improves proteinuria and serum urea nitrogen, overall ameliorating immune-mediated glomerulonephritis and renal dysfunction. Overall, we propose that this biogenic amine is a crucial component of tryptophan-mediated immune tolerance.